1. Field of the Invention
The present invention relates to a light-measuring system and method thereof. More particularly, the present invention relates to a light-measuring method and a light-measuring system with a look-up table based on a light spectrum model.
2. Description of the Prior Art
In prior art, a to-be-measured light may be measured according to the roles developed by the Commission Internationale de l'Eclairage (CIE) in 1931. The to-be-measured light is measured by the light-measuring device to obtain the tri-stimulus value. Then, the color coordinates will be obtained. However, it is difficult to manufacture the optical filters which meet three standard color-matching functions XS(λ), YS(λ) and ZS(λ). In fact, the actual color-matching functions of the light-measuring device shall be considered that the responsivity R(λ) is uneven. In other words, the actual color-matching functions can be defined as Xi(λ)=Ri(λ)Ti(λ), wherein Ti(λ) is a penetration function of the optical filter, i=1˜3. If the variations of the elements are considered, it is difficult to let Xi(λ) equal to XS(λ), YS(λ) and ZS(λ).
Thus, the variations of the light-sensing element cannot be removed. In fact, the actual color-matching functions shall be normalized in measurement for decreasing the variations of the actual color-matching functions and the standard color-matching functions. In practice, a known light may be normalized. For example, an regulation constants Ai of an A light (Ai=∫λ1λ2SA(λ) Xi(λ)dλ/∫λ1λ2SA(λ)Xi(λ)dλ, wherein i=1˜3 are the said standard color-matching functions XS(λ), YS(λ) and ZS(λ). Thus, the stimulus values obtained by measuring the to-be-measured light, or the stimulus values calculated by the regulation constants multiplied by the integration of the actual color-matching functions and the light spectrum, have errors which cannot be avoided. For the to-be-measured light with large waviness width, such as white light, the errors can be accepted. However, for the to-be-measured light with small waviness width, such as monochromatic light, the errors cannot be ignored.
A four-color matrix method developed by Yoshihiro Ohno in 1997 (IS&T fifth color image conference 1997), is applied to correct three regulation coefficients by using the white light combined by the red light, green light and blue light. Accordingly, the chromaticity of the monochromatic light can be measured accurately. However, for the light spectrum with large variations, the errors of the light cannot be ignored.
To sum up, the errors of the light-measuring device cannot be removed in prior art. Additionally, if the variations of light spectrum used by the to-be-measured light and the normalization are too large, the errors of measuring the color coordinates will become lager.